The only manner of resolving this is to go under the French yoke of proof of life. These are French pensions and that is therefore inevitable. The French pension administration like any other do not appreciate paying out money to the dead - as they have to recover it.
The French pension administrators should have sent you proof of life certificates to be filled out and attested by one of the following:
- Local council / court
- Registry office, civic centre
- Local police station
- Commissioner for oaths
- Solicitor / Lawyer/ Barrister
- Notary public
The general approach and procedure is set out at the following link: https://uk.ambafrance.org/The-life-certificate-attestation-d-existence
If the pension providers have not sent you a form, there a link to a Cerfa form which can be used, but you may find that some pension providers will prefer their own.
You will need to contact the consulate if she is bed ridden or otherwise incapable and cannot attend on one of the certifying individuals.
Does the lady have French nationality? If she does, you may wish to go through the procedure of registering her as a French national resident in the UK at the French consulate in London. If you are able to go through that route, then the issues will rapidly become clearer in the sense that there is a procedure to follow and the Consulate staff are generally helpful.
Hope this helps et Bon courage.
Peter Harris